Halogen substitution of aromatic cations for phase transition control and high-efficiency luminescence in 0D...

Zero-dimensional (0D) organic-inorganic hybrid manganese halides are emerging as attractive materials for optoelectronic applications, owing to their structural versatility, low toxicity, and excellent luminescence properties. Nevertheless, achieving simultaneous control over phase transition behavior and photoluminescence quantum yield (PLQY) through molecular-level design remains challenging. In this work, two 0D manganese-based hybrid compounds with distinct halogen substitution patterns, (2,5-DFBTP)₂MnBr₄ (1) and (2-Cl-5-FBTP)₂MnBr₄ (2) (2,5-DFBTP = (2,5-difluorobenzyl)trimethylphosphonium; 2-Cl-5-FBTP = (2-chloro-5-fluorobenzyl)trimethylphosphonium), are successfully synthesized and systematically investigated. By rationally tuning spatial distribution of halogen substituents on the organic cation, concurrent modulation of the phase transition energy barrier and (Photoluminescence Quantum Yield) PLQY is realized. Compound 1 exhibits a reversible phase transition at 428.5 K, whereas compound 2 shows no detectable phase transition across the measured temperature range. At the same time, the PLQY is markedly enhanced from 58.35% to 93.33%, accompanied by a pronounced narrowing of the emission bandwidth and improved color purity. Detailed structural analysis reveals that the variation in halogen substitution not only alters the phase transition energy barrier but also optimizes luminescence performance by regulating the Mn-Mn distance, introducing C-Cl⋯Br halogen bonding interactions to reinforce lattice rigidity. This work demonstrates the effectiveness of halogen synergy engineering in tailoring the structure-phase transition-luminescence relationship, and provides a viable strategy for the development of high-performance manganese-based emitters and multifunctional optoelectronic materials.